Detergent products comprising anionic and/or nonionic surfactants which are particularly suitable for fabric washing generally have a tendency in use to produce excessive foam. This can be a problem particularly with drum-type washing machines, and it is accordingly usual to include an antifoam agent in the detergent formulation to reduce or eliminate this tendency to produce excessive foam.
Excessive foam derived from detergent products containing anionic and/or nonionic surfactants can for example be controlled to a limited extent by the addition of soap, or by the incorporation of certain oils, such as hydrocarbons or silicone oils, or particles such as hydrophobic silica, or mixtures of such materials.
It has for example been proposed in EP 71 481A (Unilever) to provide an antifoam ingredient comprising a core of gelatinised starch having a mixture of a silicone oil and hydrophobic silica sorbed thereon as antifoam active materials. EP 109 247A (Unilever) discloses an antifoam ingredient comprising a core of gelatinised starch carrying a mixture of hydrocarbon oils and waxes and hydrophobic silica.
Although such antifoam particles are highly effective in reducing the tendency of a freshly manufactured detergent product to produce excessive foam, there is still a substantial risk that the antifoam activity will diminish on storage in a detergent powder. This is believed to be due to migration of some of the antifoam active substances, particularly those of an oily nature, from the core material into the surrounding powder or even the packaging material. This can happen more rapidly when such powders are stored at temperatures above room temperature (20.degree. C.), and after a period of storage of a few weeks the activity of the antifoam agent can be severely impaired.
It is accordingly desirable to incorporate the antifoam agents in the detergent powder during manufacture in a form in which they are protected against premature deactivation during storage, so that their effectiveness in controlling excessive foam production, both at low and at high washing temperatures, is not diminished.
FR 2 462 184A (Eurand-France) discloses an antifoam ingredient in the form of granules in which a core of silicone oil is encapsulated by a shell or coating of hydrophilic water-soluble crystalline material, which is preferably a sugar such as lactose or a salt such as sodium chloride. The hard crystalline outer shell of the granules is formed by a recrystallisation process: granules of silicone oil and the hydrophilic coating material are covered with excess powdered coating material and wetted, for example with 3.2% or 6.67% by weight of water, to dissolve out a superficial part of the coating material, and the water is then evaporated off so that a hard film of recrystallised coating material is formed. The graules obtained are essentially in the form of encapsulates having a core of silicone oil completely surrounded by a shell of crystalline coating material. Although starches and starch derivatives are disclosed as usable in the process, it is believed that only highly crystalline starches would in fact exhibit appropriate dissolution and crystallisation properties.
We have now discovered that it is possible to produce starch-based antifoam granules having a reduced tendency to deactivation in storage, while maintaining excellent foam control at both low and high wash temperatures, using a simpler process than that of FR 2 462 184A discussed above. The antifoam granules of the present invention utilise as core material a pregelatinised amorphous starch containing a certain amount (generally about 10%) of water: during the manufacture of the granules, the starch is swollen in a controlled hydration step to entrap the antifoam active substances within, while the granules themselves remain dry. In contrast to the disclosure of FR 2 462 184A mentioned above, the starches used in accordance with the invention are essentially amorphous both before and after the controlled hydration step, and are not dissolved and recrystallised when water is added, but instead swell: the water added in the controlled hydration step is retained within the swollen starch and need not be removed by evaporation as in FR 2 462 184A. It is believed that the pregelatinised amorphous starches used in the present invention could not be used in the process described in FR 2 462 184A.
When incorporated in a detergent powder product the antifoam granules of the present invention show a reduced tendency towards premature loss during storage of any oily antifoam active substance, by migration from within the granules into the dry powder product or even into the packaging. Oily antifoam active substance can be retained within the antifoam granule until the product is contacted with water, for example during the washing of fabrics, when release of the antifoam active substance can be triggered to produce effective control of foam generated by the detergent active present in the detergent powder product as the wash temperature rises. The effectiveness of the antifoam ingredient is thereby retained until it is needed at the point of use.